Signal propagation and the dispersion relations of bubbly water

Abstract

The physics behind the extreme variations of the phase velocity of acoustic wave propagation in a bubbly liquid as a function of frequency have been addressed theoretically. Until recently there has not been a concerted experimental effort to validate this work over the rather large parameter landscape covered by the theories. To this end there there have been several sets of experiments conducted at the Naval Research Laboratory’s Salt-Water Tank Facility aimed in part at validating these theories. In order to properly measure phase velocities in a semi-free field environment, one must be able to accurately measure the arrival of a short acoustic pulse. This leads naturally to the question of what one measures as the velocity of sound in a highly dispersive medium where the group velocity can indeed have infinite, zero, or negative values. We discuss this and its relationship to work in other fields of physics. [Work supported by ONR.]